1. Field of the Invention
This invention relates to a III nitride epitaxial substrate, an epitaxial substrate for III nitride element and a III nitride element, particularly a III nitride epitaxial substrate suitable for a semiconductor nitride element such as a photonic device, an electronic device or a field emitter, a III nitride element such as a photonic device made of the III nitride film epitaxial film, and an epitaxial substrate for the III nitride element.
2. Related Art Statement
III nitride films are used as semiconductor films for light-emitting diodes and electronic devices, and recently get attention as semiconductor films for high speed IC chips. Particularly, Al-including III nitride films get attention as field emitter materials.
Such a III nitride film is formed on an epitaxial substrate, for example, which has an underfilm epitaxially grown on a given base material. A sapphire single crystal is employed as the base material because it is not expensive and easily available.
The underfilm is preferably made of an Al-including III nitride film in order to facilitate the epitaxial growth of the III nitride film to be formed Moreover, since such an Al-including III nitride film has a larger bandgap, if it is formed between a base material and a given III nitride film, it can enhance the efficiency of the resultant semiconductor element.
The epitaxial substrate is set on a susceptor installed in a given reactor, and heated to a predetermined temperature with a heater built in or out of the susceptor. Then, a III metallic supply source, a nitrogen supply source and another element supply source if desired are introduced into the reactor with a carrier gas, and supplied onto the epitaxial substrate to fabricate the III nitride film by an MOCVD method.
In the case of the use of the epitaxial substrate, a large amount of misfit dislocations may be created due to the difference in lattice constant between the sapphire single crystal base material and the Al-including III nitride underfilm, and propagated as penetrating dislocations through the III nitride underfilm to reach the surface of the epitaxial substrate. If the III nitride film is made on the epitaxial substrate, a large amount of dislocations may be created in the III nitride film, originated from the propagated misfit dislocations.
The above-mentioned similar phenomenon can be observed when a Ga-including or another III nitride underfilm as well as the Al-including III nitride underfilm is formed on the sapphire single crystal base material.
In other words, in the case of the use of the sapphire single crystal base material, only a low crystal quality III nitride film including a relatively large amount of dislocations can be formed, so that if a semiconductor light-emitting element is fabricated by utilizing the low crystal quality m nitride film, the luminous efficiency of the semiconductor element is deteriorated. And if a electronic device element such as HEMT, HBT is fabricated by utilizing the low crystal quality III nitride film, electrical mobility goes down or leak electric current increases. As a result, the semiconductor element can not exhibit the inherent performances as designed.